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Abstract

Nocturnal behaviors and sleep patterns of nesting passerines remain largely undocumented in the field and are important to understanding responses to environmental pressures such as predation. We used nocturnal video recordings to describe activity and quantify behaviors of females with nestlings of four shrub land bird species and three grassland bird species (n = 19 nests). Among the shrubland birds, Blue-winged Warbler (Vermivora pinus), Prairie Warbler (Setophaga discolor), and Indigo Bunting (Passerina cyanea) returned to the nest for the night at the same time, around sunset. Among the grassland birds, Eastern Meadowlark (Stumella magna) returned the earliest before sunset and Grasshopper Sparrow (Ammodramus savannarum) returned the latest after sunset. All species exhibited "back sleep" with the bill tucked under scapular feathers, and individuals awoke frequently for vigils or "peeks" at their surroundings. Sleep of all species was disrupted by nestling activity. Average duration of sleep bouts varied from 6 min (Grasshopper Sparrow) to 28 min (Blue-winged Warbler; Field Sparrow, Spizella pusilla). Mean overnight duration on the nest varied from 6.4 hr (Field Sparrow) to 8.8 hr (Indigo Bunting). On average, adults woke in the morning (the last waking before departing the nest) 20-30 min before sunrise. The first absence from the nest in the morning was short for all species, and nestlings were fed within 12 min of a parent's departure. Our study highlights the need for further video research on sleep patterns of nesting birds in the field to better understand basic natural history, energetic cost-benefits of sleep, and behavioral adaptations to environmental pressures.